This patent application is co-pending with one related patent application entitled xe2x80x9cFAN ROTOR WITH CONSTRUCTION AND SAFETY PERFORMANCE OPTIMIZATIONxe2x80x9d (Navy Case No. 82986), filed on the same date and owned by the same assignee as this patent application.
The invention relates generally to vane-axial fan assemblies, and more particularly to a high-pressure axial flow fan assembly that is aerodynamically more efficient and quieter than current designs.
U.S. Navy ships incorporating the Collective Protection System (CPS) in their ventilation system design use vane-axial (in-line duct) supply fans that are required to develop pressures that are substantially greater than those developed by conventional ventilation system fans. These CPS high-pressure ventilation supply fans are designed to overcome normal system pressure losses as well as pressure losses associated with a series of specialized air filters. In addition, the typical CPS supply fan must also be capable of maintaining a pressurized zone within the ship""s hull.
Current U.S. Navy CPS ventilation systems use conventional fan technology in terms of rotor blade and stator vane configurations. That is, rotor blades are typically based on profiles of blended circular arcs that are not necessarily the most efficient from an aerodynamic perspective, and not the quietest from an aero-acoustic perspective. Aerodynamic inefficiencies and noise sources in the high-pressure fan assemblies include rotor blade vortex generation, flow separation from both rotor blades and stator vanes, and the interaction of the air as it transitions from rotor blades to stator vanes. The conventional solution for a low efficiency fan design involves the use of a higher horsepower fan motor to perform the aerodynamic work. The conventional solution used to keep the airborne noise levels within the required U.S. Navy specification for allowable space noise levels involves the use of a greater amount of acoustic attenuation material. Neither of these conventional solutions is desirable.
Accordingly, it is an object of the present invention to provide a fan assembly having increased efficiencies and lower noise levels as compared to current high-pressure fan designs.
Another object of the present invention is to provide a fan assembly having an improved rotor blade design.
Still another object of the present invention is to provide a fan assembly having an improved rotor-to-stator configuration to reduce noise as air transitions from rotor blades to stator vanes.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a fan assembly includes a hub defining an axis of rotation. A plurality of rotor blades are disposed circumferentially around and extend radially outward from the hub. Each rotor blade is constructed to define a straight-ruled leading edge that extends outward from the hub. There is unequal angular spacing between leading edges of adjacent ones of the rotor blades. Each rotor blade has a trailing edge that extends from the hub at a skew angle measured in a radial plane of the hub with respect to a first line extending radially outward from the axis of rotation. Each rotor blade has an axial chord length defined across a central portion thereof parallel to the hub""s axis of rotation. The plurality of rotor blades further defines a solidity of greater than 1. A plurality of stator vanes are disposed circumferentially around and extend radially from a frame. There are a lesser number of stator vanes than rotor blades. Each stator vane has a leading edge that extends from the frame at: i) an inclined angle measured in the radial plane with respect to a second line extending radially outward from the axis of rotation, and ii) a lean angle measured in an axial plane of the frame with respect to a third line extending radially outward from the axis of rotation. The frame with its stator vanes is positioned adjacent hub and rotor blades such that an axial gap is defined between the trailing edge of the rotor blades and the leading edge of the stator vanes. The axial gap increases with radial distance from the hub as defined by the skew angle and inclined angle. The axial gap is a minimum of the rotor blade""s axial chord length.